THE MINERALS OF IDAHO 337 



is 09' short of the value given by Dana. For the interfacial angle 

 o : o'" the value given by Dana is 40° 29' and the angles obtained 

 on the Idaho crystals vary from 36° 34' to 42° 45'. The variation 

 is in part probably due to splitting of the crystals parallel to (010) 

 and in part due to vicinal forms in the same zone. 



The Idaho Ilvaite has been analyzed by Hillebrand with the fol- 

 lowing results. 61 



Analysis of Ilvaite, Golconda mine 



(W. F. Hillebrand, analyst) 



Per cent 



Silica (Si0 8 ) 29. 16 



Alumina ( A1 2 3 ) .52 



Ferric iron (Fe 2 3 ) 20. 40 



Ferrous iron (FeO) 29. 14 



Manganese oxide (MnO) 5. 51 



Lime (CaO) 13. 02 



Magnesia (MgO) . 15 



Soda (NaoO) . 08 



Water (H 2 0) below 110° C . 15 



Water (H 2 0) above 110° C 2.64 



Total 100.77 



In the Idaho ilvaite cleavage is present but not conspicuous 

 parallel to &(010). The fracture is uneven, hardness 5.75; specific 

 gravity 4.059 (Hillebrand). The luster is vitreous and not sub- 

 metallic as described from other localities; color, black; streak black 

 with faint brownish tinge. The mineral is rather difficultly fusible 

 before the blowpipe and upon fusion it intumesces slightly and yields 

 a black magnetic bead. It is readily soluble in hot hydrochloric 

 acid, yielding an amber solution which gelatinizes. 



Several unsuccessful attempts were made to cut oriented sections 



of the crystals for optical examination, but the mineral is too opaque 



to transmit sufficient light in the thinnest sections which could be 



ground. 



CALAMINE (423) 



Basic zinc silicate, H 2 0.2ZnO.Si0 2 Orthorhombic, hemimorphic. 



Calamine is a secondary zinc mineral always occurring as an altera- 

 tion product of sphalerite in the oxidized portions of zinc-bearing 

 ore deposits, where it is commonly associated with smithsonite and 

 usually also with limonite and cerusite. The several Idaho occur- 

 rences are not important as zinc ores although fair mineral speci- 

 mens have been obtained from each. 



CASSIA COUNTY 



Bluish-white to white radiating sheaves and druses of minute thin 

 tabular calamine crystals occur in cavities in a chalky cellular white 

 rock from the Black Pine mining district in Cassia County (Cat. No. 

 89,130, U.S.N.M.). 



•" W. F. Hillebrand. U. S. Geol. Survey Bull. 591, p. 318. 



